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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Impact of urine concentration adjustment method on associations between urine metals and estimated glomerular filtration rates (eGFR) in adolescents

Positive associations between urine toxicant levels and measures of glomerular filtration rate (GFR) have been reported recently in a range of populations. The explanation for these associations, in a direction opposite that of traditional nephrotoxicity, is uncertain. Variation in associations by urine concentration adjustment approach has also been observed. Associations of urine cadmium, thallium and uranium in models of serum creatinine- and cystatin-C-based estimated GFR (eGFR) were examined using multiple linear regression in a cross-sectional study of adolescents residing near a lead smelter complex. Urine concentration adjustment approaches compared included urine creatinine, urine osmolality and no adjustment. Median age, blood lead and urine cadmium, thallium and uranium were 13.9 years, 4.0 μg/dL, 0.22, 0.27 and 0.04 g/g creatinine, respectively, in 512 adolescents. Urine cadmium and thallium were positively associated with serum creatinine-based eGFR only when urine creatinine was used to adjust for urine concentration (β coefficient=3.1 mL/min/1.73 m{sup 2}; 95% confidence interval=1.4, 4.8 per each doubling of urine cadmium). Weaker positive associations, also only with urine creatinine adjustment, were observed between these metals and serum cystatin-C-based eGFR and between urine uranium and serum creatinine-based eGFR. Additional research using non-creatinine-based methods of adjustment for urine concentration is necessary. - Highlights: • Positive associations between urine metals and creatinine-based eGFR are unexpected. • Optimal approach to urine concentration adjustment for urine biomarkers uncertain. • We compared urine concentration adjustment methods. • Positive associations observed only with urine creatinine adjustment. • Additional research using non-creatinine-based methods of adjustment needed.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Concentrating photovoltaic retrofit for existing parabolic trough solar collectors: Design, experiments, and levelized cost of electricity

Photovoltaics and concentrating solar thermal power are two ways for generating electricity from sunlight, albeit through different methods. Parabolic trough style powerplants represent 3.6 GW of electricity production, but many of these plants are aging and being replaced with photovoltaics. An alternative option that could be employed to leverage the sunk capital cost associated with the primary optics would be the design of a pure photovoltaic retrofit working within the existing plant architecture. Here, a secondary optical concentrator is designed to use the existing primary optics of a parabolic trough type solar thermal powerplant. The design is a v-shaped secondary concentrator resulting in a predicted concentration ratio on a 20 mm wide target of 94. The concentrating photovoltaic receiver for retrofit of an RP-3 based parabolic trough has been constructed using multi-junction concentrator photovoltaic cells and experimentally demonstrated here for the first time. Calculated performance of the cells based on cell specifications should result in 31% efficiency at 85 °C. On-sun efficiencies were measured at an average value of 21% with operational temperatures between 55 and 120 °C. Levelized cost of electricity calculations predict the system to have the potential to be below 7¢/kWh based on predicted efficiencies and 13¢/kWh based on the measured values at cell costs of $5/cm 2 .

14 SOLAR ENERGY↗
DOE OSTI2018

Automated concentration of [ 18 F]fluoride into microliter volumes

Concentration of [ 18 F]fluoride has been mentioned in literature, however, reports have lacked details about system designs, operation, and performance. Here, we describe in detail a compact, fast, fully-automated concentration system based on a micro-sized strong anion exchange cartridge. The concentration of radionuclides enables scaled-up microfluidic synthesis. Our system can also be used to provide highly concentrated [ 18 F]fluoride with minimal water content. We demonstrate how the concentrator can produce varying concentrations of [ 18 F]fluoride for the macroscale synthesis of N-boc-5-[ 18 F]fluoroindole without an azeotropic drying process, while enabling high starting radioactivity. By appropriate choice of solid-phase resin, flow conditions, and eluent solution, we believe this approach can be extended beyond [ 18 F]fluoride to other radionuclides.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Differential concentration-specific effects of caffeine on cell viability, oxidative stress, and cell cycle in pulmonary oxygen toxicity in vitro

Highlights: • Caffeine at 0.05 mM decreases oxidative stress in hyperoxia. • Caffeine at 1 mM decreases cell viability, increases oxidative stress in hyperoxia. • Caffeine at 1 but not 0.05 mM, abrogates hyperoxia-induced G2/M arrest. - Abstract: Caffeine is used to prevent bronchopulmonary dysplasia (BPD) in premature neonates. Hyperoxia contributes to the development of BPD, inhibits cell proliferation and decreases cell survival. The mechanisms responsible for the protective effect of caffeine in pulmonary oxygen toxicity remain largely unknown. A549 and MLE 12 pulmonary epithelial cells were exposed to hyperoxia or maintained in room air, in the presence of different concentrations (0, 0.05, 0.1 and 1 mM) of caffeine. Caffeine had a differential concentration-specific effect on cell cycle progression, oxidative stress and viability, with 1 mM concentration being deleterious and 0.05 mM being protective. Reactive oxygen species (ROS) generation during hyperoxia was modulated by caffeine in a similar concentration-specific manner. Caffeine at 1 mM, but not at the 0.05 mM concentration decreased the G2 arrest in these cells. Taken together this study shows the novel funding that caffeine has a concentration-specific effect on cell cycle regulation, ROS generation, and cell survival in hyperoxic conditions.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Using concentrating-solar-power plants as economic carbon-free capacity resources

Deep decarbonization of electricity systems raises concerns about the need for generating capacity that can maintain reliable energy supply. Given this concern, we explore the ability of concentrating-solar-power plants with thermal energy storage to provide a carbon-free source of such capacity. We develop an approach to assessing the capacity contribution of concentrating-solar-power plants that considers future systems. Such considerations are important, because of potential differences in net-load patterns compared to today (e.g., due to higher renewable-energy penetrations). Using historical data spanning an 18-year period, we demonstrate that concentrating-solar-power plants with thermal energy storage can provide this necessary capacity with little impact on their financial viability. We examine the impact of myopic decisions and imperfect foresight of future system conditions on the operation of concentrating-solar-power plants and the resultant impact on their capacity contributions. We find that imperfect foresight can have limited impacts on such a use of concentrating-solar-power plants, so long as proper forecasting techniques are developed and used. Overall, our work shows that concentrating-solar-power plants with thermal energy storage may have a role to play in delivering reliable electricity supply in a decarbonized energy system.

14 SOLAR ENERGY↗
DOE OSTI2020

Off-design performance of molten salt-driven Rankine cycles and its impact on the optimal dispatch of concentrating solar power systems

This paper presents a model for improving off-design performance predictions for molten salt-driven Rankine power cycles, such as in concentrating solar power tower applications. The model predicts cycle off-design performance under various boundary conditions, including molten salt inlet temperature, mass flow rate, and ambient temperature. The model is validated using industry performance data and benchmarked with results from the literature. A complete concentrating solar power plant, inclusive of solar heliostat field and receiver, is then considered, by implementing the Rankine cycle off-design performance results into the National Renewable Energy Laboratory’s System Advisor Model software, which includes a tool that determines optimal power production schedules. The work improves upon the current System Advisor Model by updating off-design performance characteristics. A case study demonstrates the impact of cycle off-design behavior on annual performance for a stand-alone concentrating solar power system and a concentrating solar power-photovoltaic hybrid system. In addition, we demonstrate how cycle off-design performance influences optimal operator dispatch decisions and, thereby, overall system design and economics. We conclude that off-design cycle performance impacts “optimal” sub-system sizing, especially for a concentrating solar power-photovoltaic hybrid configuration in which concentrating solar power must dispatch in conjunction with photovoltaic generation.

14 SOLAR ENERGY↗
DOE OSTI2018

Non-monotonic effects of market concentration on prices for residential solar photovoltaics in the United States

We report that emerging renewable energy markets may become more concentrated over time as the most efficient firms accumulate market share. The effects of this market concentration on prices are tested using a rich dataset of residential solar photovoltaic (PV) systems in the United States. A novel hypothesis is explored that the effects of market concentration may be non-monotonic. Prices may decline in market concentration due to efficiency gains associated with returns to scale but increase in concentration in already concentrated markets due to increasing market power. Finally, the results of an econometric model provide evidence to support the non-monotonic hypothesis. However, the data suggest that the relationship between prices and firm scale is nuanced, and that both large- and small-scale PV installers may wield efficiency advantages.

14 SOLAR ENERGY↗
DOE OSTI2016

High feather mercury concentrations in the wandering albatross are related to sex, breeding status and trophic ecology with no demographic consequences

Hg can affect physiology of seabirds and ultimately their demography, particularly if they are top consumers. In the present study, body feathers of >200 wandering albatrosses from Possession Island in the Crozet archipelago were used to explore the potential demographic effects of the long-term exposure to Hg on an apex predator. Variations of Hg with sex, age class, foraging habitat (inferred from δ{sup 13}C values), and feeding habits (inferred from δ{sup 15}N values) were examined as well as the influence of Hg on current breeding output, long-term fecundity and survival. Wandering albatrosses displayed among the highest Hg feather concentrations reported for seabirds, ranging from 5.9 to 95 µg g{sup −1}, as a consequence of their high trophic position (δ{sup 15}N values). These concentrations fall within the same range of those of other wandering albatross populations from subantarctic sites, suggesting that this species has similar exposure to Hg all around the Southern Ocean. In both immature and adult albatrosses, females had higher Hg concentrations than males (28 vs. 20 µg g{sup −1} dw on average, respectively), probably as a consequence of females foraging at lower latitudes than males (δ{sup 13}C values). Hg concentrations were higher in immature than in adult birds, and they remained fairly constant across a wide range of ages in adults. Such high levels in immature individuals question (i) the frequency of moult in young birds, (ii) the efficiency of Hg detoxification processes in immatures compared to adults, and (iii) importantly the potential detrimental effects of Hg in early life. Despite very high Hg concentrations in their feathers, neither effects on adults' breeding probability, hatching failure and fledgling failure, nor on adults' survival rate were detected, suggesting that long-term bioaccumulated Hg was not under a chemical form leading to deleterious effects on reproductive parameters in adult individuals. - Highlights: • Immature albatrosses had higher feather Hg concentrations than adults. • Foraging habitat influenced Hg bioaccumulation as a result of male and female segregation. • No carry-over effects were detected on reproductive parameters.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Blood cadmium concentrations and environmental exposure sources in newcomer South and East Asian women in the Greater Toronto Area, Canada

Background: Immigrant women are often identified as being particularly vulnerable to environmental exposures and health effects. The availability of biomonitoring data on newcomers is limited, thus, presenting a challenge to public health practitioners in the identification of priorities for intervention. Objectives: In fulfillment of data needs, the purpose of this study was to characterize blood concentrations of cadmium (Cd) among newcomer women of reproductive age (19–45 years of age) living in the Greater Toronto Area (GTA), Canada and to assess potential sources of environmental exposures. Methods: A community-based model, engaging peer researchers from the communities of interest, was used for recruitment and follow-up purposes. Blood samples were taken from a total of 211 newcomer women from South and East Asia, representing primary, regional origins of immigrants to the GTA, and environmental exposure sources were assessed via telephone survey. Metal concentrations were measured in blood samples (diluted with 0.5% (v/v) ammonium hydroxide and 0.1% (v/v) octylphenol ethoxylate) using a quadrupole ICP-MS. Survey questions addressed a wide range of environmental exposure sources, including dietary and smoking patterns and use of nutritional supplements, herbal products and cosmetics. Results: A geometric mean (GM) blood Cd concentration of 0.39 µg/L (SD:±2.07 µg/L) was determined for study participants (min/max: <0.045 µg /L (LOD)/2.36 µg/L). Several variables including low educational attainment (Relative Ratio (RR) (adjusted)=1.50; 95% CI 1.17–1.91), milk consumption (RR (adjusted)=0.86; 95% CI 0.76–0.97), and use of zinc supplements (RR (adjusted)=0.76; 95% CI 0.64–0.95) were observed to be significantly associated with blood Cd concentrations in the adjusted regression model. The variable domains socioeconomic status (R{sup 2}{sub adj}=0.11) and country of origin (R{sup 2}{sub adj}=0.236) were the strongest predictors of blood Cd. Conclusion: Blood Cd concentrations fell below those generally considered to be of human health concern. However, negative health effects cannot be entirely excluded, especially for those that fall in the upper percentile range of the distribution, given the mounting evidence for negative health outcomes at low environmental exposure concentrations. - Highlights: • Blood Cd and exposure sources were assessed for 211 newcomer women in Toronto. • Blood Cd was slightly elevated compared to that in Canadian-born populations. • SES and country of origin were the strongest predictors of blood Cd. • Intake of essential micronutrients is a likely important modulator of blood Cd. • Identified need for more research on newcomers as a function of country of origin.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Effects of sulfurization time and H{sub 2}S concentration on electrical properties of Cu{sub 2}ZnSnS{sub 4} films prepared by sol–gel method

Highlights: • Cu{sub 2}ZnSnS{sub 4} (CZTS) films were prepared by sol–gel method following sulfurization. • The sulfurization time and H{sub 2}S concentration have the effects on the electrical properties. • The tin loss is increased with the increasing of the sulfurization time. • The secondary phases like ZnS make the electrical properties worse. • The CZTS films sulfurized at 5% H{sub 2}S for 90 min had the best electrical properties. - Abstract: Cu{sub 2}ZnSnS{sub 4} (CZTS) thin films have been successfully deposited by a sol–gel method and sulfurization process. The properties of the films were investigated by varying sulfurization time and H{sub 2}S concentration. X-ray diffraction and Raman spectra analyses revealed the formation of CZTS films with a tetragonal type kesterite structure. With increasing the sulfurization time and H{sub 2}S concentration, the intensity of the kesterite (1 1 2) peak became sharper. The stoichiometric ratios of the CZTS films were different from the precursors, which was due to Sn loss during the sulfurization process. The electrical resistivity and mobility of the films increased while the carrier concentration decreased with increasing the sulfurization time. The CZTS thin films sulfurized at 5% H{sub 2}S concentration for 90 min had the best opto-electrical properties with E{sub g} of 1.41 eV, resistivity of 3.64 Ω cm, carrier concentration of 1.11 × 10{sup 18} cm{sup −3} and mobility of 1.54 cm{sup 2}/(V s) at room temperature for PV application.

36 MATERIALS SCIENCE↗
DOE OSTI2026

A mathematical design framework for membrane pre-concentration in energy-efficient recovery of fermentation products

Due to the dilute nature of products manufactured via fermentation and cell-free bioprocessing, dewatering is a common unit operation in downstream processing (DSP) for bioproduct recovery, but it is typically energy intensive. To improve DSP energy efficiency for bio-based small molecules, integrating high-pressure membrane pre-concentration is a promising process option. However, this approach is typically constrained by a tradeoff between concentration factor (CF) and product recovery (PR), namely increasing the CF typically results in greater product loss, and vice versa. Here we developed a model that enables process design guidelines to: (i) identify scenarios in which the additional energy consumption and product loss from membrane pre-concentration are justified for use in DSP, and (ii) determine the optimal CF that minimizes process specific energy consumption. We compared the energy consumption of high-pressure membrane-integrated processes to evaporation-only processes and applied the model to an experimental case study for the separation and purification of butyric acid from Clostridium tyrobutyricum fermentation using an in situ product recovery (ISPR) process. The model estimated that integrating a tangential-flow reverse osmosis (RO) pre-concentration unit could reduce process energy consumption up to 45%. The use of advanced membrane pre-concentration technologies, such as negative rejection membranes and organic solvent reverse osmosis (OSRO), have the potential to further reduce the overall process specific energy consumption up to 96%, projected based on modeling. Overall, membrane pre-concentration, especially when strategically integrated prior to an evaporation step with optimized process conditions, holds significant potential for improving DSP energy efficiency, particularly in applications requiring substantial solvent removal for product recovery from dilute mixtures.

09 BIOMASS FUELS↗
DOE OSTI2013

Proximal renal tubular injury in rats sub-chronically exposed to low fluoride concentrations

Fluoride is usually found in groundwater at a very wide range of concentration between 0.5 and 25 ppm. At present, few studies have assessed the renal effects of fluoride at environmentally relevant concentrations. Furthermore, most of these studies have used insensitive and nonspecific biomarkers of kidney injury. The aim of this study was to use early and sensitive biomarkers to evaluate kidney injury after fluoride exposure to environmentally relevant concentrations. Recently weaned male Wistar rats were exposed to low (15 ppm) and high (50 ppm) fluoride concentrations in drinking water for a period of 40 days. At the end of the exposure period, kidney injury biomarkers were measured in urine and renal mRNA expression levels were assessed by real time RT-PCR. Our results showed that the urinary kidney injury molecule (Kim-1), clusterin (Clu), osteopontin (OPN) and heat shock protein 72 excretion rate significantly increased in the group exposed to the high fluoride concentration. Accordingly, fluoride exposure increased renal Kim-1, Clu and OPN mRNA expression levels. Moreover, there was a significant dose-dependent increase in urinary β-2-microglobulin and cystatin-C excretion rate. Additionally, a tendency towards a dose dependent increase of tubular damage in the histopathological light microscopy findings confirmed the preferential impact of fluoride on the tubular structure. All of these changes occurred at early stages in which, the renal function was not altered. In conclusion using early and sensitive biomarkers of kidney injury, we were able to found proximal tubular alterations in rats sub-chronically exposed to fluoride. - Highlights: • Exposure to low concentrations of fluoride induced proximal tubular injury • Increase in urinary Kim-1, Clu, OPN and Hsp72 in 50 ppm fluoride-exposed group • Increase in urinary B2M and CysC in 15 and 50 ppm fluoride-exposed groups • Fluoride exposure increased renal Kim, Clu and OPN mRNA expression levels. • Fluoride increased kidney injury biomarkers at stages where eGFR was unaltered.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Preservation of high glycolytic phenotype by establishing new acute lymphoblastic leukemia cell lines at physiologic oxygen concentration

Cancer cells typically exhibit increased glycolysis and decreased mitochondrial oxidative phosphorylation, and they continue to exhibit some elevation in glycolysis even under aerobic conditions. However, it is unclear whether cancer cell lines employ a high level of glycolysis comparable to that of the original cancers from which they were derived, even if their culture conditions are changed to physiologically relevant oxygen concentrations. From three childhood acute lymphoblastic leukemia (ALL) patients we established three new pairs of cell lines in both atmospheric (20%) and physiologic (bone marrow level, 5%) oxygen concentrations. Cell lines established in 20% oxygen exhibited lower proliferation, survival, expression of glycolysis genes, glucose consumption, and lactate production. Interestingly, the effects of oxygen concentration used during cell line initiation were only partially reversible when established cell cultures were switched from one oxygen concentration to another for eight weeks. These observations indicate that ALL cell lines established at atmospheric oxygen concentration can exhibit relatively low levels of glycolysis and these levels are semi-permanent, suggesting that physiologic oxygen concentrations may be needed from the time of cell line initiation to preserve the high level of glycolysis commonly exhibited by leukemias in vivo. - Highlights: • Establishing new ALL cell lines in 5% oxygen resulted in higher glycolytic expression and function. • Establishing new ALL cell lines in 5% oxygen resulted in higher proliferation and lower cell death. • The divergent metabolic phenotypes selected in 5% and 20% oxygen are semi-permanent.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Effects of varying gelatin coating concentrations on RANKL induced osteoclastogenesis

Here, we assessed the effects of varying concentrations of gelatin coating on Receptor Activator of Nuclear Factor κ-B Ligand (RANKL)-induced RAW264.7 murine macrophage differentiation into osteoclast (OC) via osteoclastogenesis. The microstructures of coating surfaces with different concentrations of gelatin were examined by scanning electron microscopy and atomic force microscopy. Increased gelatin coating concentrations led to decreased gel rigidity but increased surface adhesion force attenuated OC differentiation and the decreased actin ring formation in RANKL-induced osteoclastogenesis. The decreased actin ring formation is associated with decreased lysosomal-associated membrane protein 1 (LAMP1) activity and bone resorption in the differentiated OCs with different gelatin coating concentrations as compared to the cells differentiated without gelatin coatings. In addition, increasing concentrations of gelatin coating attenuated the medium TGF-β1 protein levels and the expression levels of TGF-β and type-I (R1) and type-II (R2) TGF-β receptors in OCs, suggesting the gelatin-induced suppression of TGF-β signaling for the regulation of RNAKL-induced OC differentiation. Taken together, these findings showed that changes in gelatin coating concentrations, which were associated with altered gel thickness and substrate rigidity, might attenuate TGF-β signaling events to modulate OC differentiation and concomitant actin ring formation and bone matrix resorption in RANKL-induced osteoclastogenesis.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Technical Performance and Economic Evaluation of Evaporative and Membrane-Based Concentration for Biomass-Derived Sugars

Several conversion pathways of lignocellulosic biomass to advanced biofuels require or benefit from using concentrated sugar syrups of 600 g/L or greater. And while concentration may seem straightforward, thermal sugar degradation and energy efficiency remain major concerns. This study evaluated the trade-offs in product recovery, energy consumption, and economics between evaporative and membrane-based concentration methods. The degradation kinetics of xylose and glucose were characterized and applied to an evaporator process simulation. Though significant sugar loss was predicted for certain scenarios due to the Maillard reaction, industrially common falling-film plate evaporators offer short residence times (<5 min) and are expected to limit sugar losses. Membrane concentration experiments characterized flux and sugar rejection, but diminished flux occurred at >100 g/L. A second step using evaporation is necessary to achieve target concentrations. Techno-economic process model simulations evaluated the overall economics of concentrating a 35 g/L sugar stream to 600 g/L in a full-scale biorefinery. A two-step approach of preconcentrating using membranes and finishing with an evaporator consumed less energy than evaporation alone but was more expensive because of high capital expenses of the membrane units.

09 BIOMASS FUELS↗
DOE OSTI2019

Impact of Salt Concentration on Nonuniform Lithium Electrodeposition through Rigid Block Copolymer Electrolytes

There is a growing demand for higher energy density lithium batteries. One approach for addressing this demand is enabling lithium metal anodes. However, nucleation and growth of electronically conductive protrusions, which cause short circuits, prevent the use of this technology with liquid electrolytes. The use of rigid solid electrolytes such as polystyrene-b-poly(ethylene oxide) electrolytes is one solution. An additional requirement for practical cells is needed to use electrolytes with high salt concentration to maximize the flux of lithium ions in the cell. The first systematic study of the effect of salt concentration on the morphology of electrodeposited lithium through a rigid block copolymer electrolyte is presented. The nature, areal density, and morphologies of defective lithium deposits created during galvanostatic cycling of lithium-lithium symmetric cells were determined using hard X-ray microtomography. Cycle life decreases rapidly with increasing salt concentration. X-ray microtomography reveals the presence of multiglobular protrusions, which are nucleated at impurity particles at low salt concentrations; here, the areal density of defective lithium deposits was independent of salt concentration. Finally, at the highest salt concentration, this density increases abruptly by a factor of about 10, and defects were also nucleated at locations where no impurities were visible.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Thermodiffusion in concentrated ferrofluids: A review and current experimental and numerical results on non-magnetic thermodiffusion

Ferrofluids are colloidal suspensions consisting of magnetic nanoparticles dispersed in a carrier liquid. Their thermodiffusive behaviour is rather strong compared to molecular binary mixtures, leading to a Soret coefficient (S{sub T}) of 0.16 K{sup −1}. Former experiments with dilute magnetic fluids have been done with thermogravitational columns or horizontal thermodiffusion cells by different research groups. Considering the horizontal thermodiffusion cell, a former analytical approach has been used to solve the phenomenological diffusion equation in one dimension assuming a constant concentration gradient over the cell's height. The current experimental work is based on the horizontal separation cell and emphasises the comparison of the concentration development in different concentrated magnetic fluids and at different temperature gradients. The ferrofluid investigated is the kerosene-based EMG905 (Ferrotec) to be compared with the APG513A (Ferrotec), both containing magnetite nanoparticles. The experiments prove that the separation process linearly depends on the temperature gradient and that a constant concentration gradient develops in the setup due to the separation. Analytical one dimensional and numerical three dimensional approaches to solve the diffusion equation are derived to be compared with the solution used so far for dilute fluids to see if formerly made assumptions also hold for higher concentrated fluids. Both, the analytical and numerical solutions, either in a phenomenological or a thermodynamic description, are able to reproduce the separation signal gained from the experiments. The Soret coefficient can then be determined to 0.184 K{sup −1} in the analytical case and 0.29 K{sup −1} in the numerical case. Former theoretical approaches for dilute magnetic fluids underestimate the strength of the separation in the case of a concentrated ferrofluid.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Effects of angular confinement and concentration to realistic solar cells

In standard solar cells, light impinges under a very small angular range, whereas the solar cell emits light into the whole half space. Due to this expansion of etendué, entropy is generated, which limits the maximal efficiency of solar cells. This limit can be overcome by either increasing the angle of incidence by concentration or by decreasing the angle of emission by an angularly confining element or by a combination of both. In an ideal solar cell with radiative recombination as the only loss mechanism, angular confinement and concentration are thermodynamically equivalent. It is shown that concentration in a device, where non-radiative losses such as Shockley-Read-Hall and Auger recombination are considered, is not equivalent to angular confinement. As soon as non-radiative losses are considered, the gain in efficiency due to angular confinement drops significantly in contrast to the gain caused by concentration. With the help of detailed balance calculations, it is furthermore shown that angular confinement can help to increase the efficiency of solar cells under concentrated sunlight even if no measurable gain is expected for the solar cell under 1-sun-illumination. Our analysis predicts a relative gain of 3.14% relative in efficiency for a realistic solar cell with a concentration factor of 500.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗